1. Technical Field of the Invention
The present invention relates to a solid oxide fuel cell module including a power generating cell constructed by sandwiching an electrolyte layer between a fuel electrode layer and an oxidant electrode layer.
Moreover, in a fuel cell including a power generating cell constructed by sandwiching a solid electrolyte layer between a fuel electrode layer and an oxidant electrode layer, the invention relates to a structure for supplying fuel gas to the fuel electrode layer and supplying oxidant gas to the oxidant electrode layer.
Moreover, the invention relates to a structure of a distributor for supplying the fuel gas and the oxidant gas to a power generating cell of a fuel cell module.
2. Description of Background Art
Conventionally, as this kind of fuel cell, a solid electrolyte fuel cell disclosed in Japanese Patent Laid-Open No. 13088/1994 is known. The publication discloses that in the solid electrolyte fuel cell, an aggregate of a laminate composed of an anode, a solid electrolyte body, and a cathode and a separator provided with a reaction gas supply pipe are alternately laminated, a groove along which fuel gas flows is formed on one surface of the separator, and a groove along which oxidant gas flows is formed on the other surface of the separator. In this fuel cell, the reaction gas supply pipe is composed of a fuel gas supply pipe and an oxidant supply pipe, at least part of which is made of a ceramic pipe such as an alumina porcelain pipe. A structure is adopted such that the fuel gas supply pipe is connected to a side surface of the separator and communicates with the groove along which the fuel gas flows, and the oxidant supply pipe is connected to a side surface of the separator and communicates with the groove along which the oxidant gas flows. Besides, the fuel gas supply pipe is connected to a fuel gas distributor made of ceramic, and the oxidant supply pipe is connected to an oxidant gas distributor made of ceramic.
In the solid oxide fuel cell constructed as stated above, since the reaction gas supply pipes are individually connected to the respective separators, a circular glass ring for sealing a circular gas manifold, which is conventionally formed for the aggregate and the separator, can be made unnecessary, and a quadrangular glass ring, which conventionally gas-seals the exterior between the aggregate and the separator, can be made unnecessary.
However, in the conventional solid electrolyte fuel cell disclosed in Japanese Patent Laid-Open No. 13088/1994, since a rib for guiding the reaction gas in a predetermined direction is formed in a ribbed porous base member of a separate plate, there has been a problem that a surface area of a power generating cell contributing to power generation is decreased by a contact area of the rib to the anode or the cathode, and power generation efficiency is lowered.
Besides, in the conventional solid electrolyte fuel cell disclosed in Japanese Patent Laid-Open No. 13088/1994, since the anode and the cathode are in contact with the ribbed porous substrate by only the rib, electron conductivity of the anode and the cathode with respect to the separate plate is low, and a reaction is apt to occur only in the vicinity of a portion where the anode and the cathode are in contact with the rib. That is, since the groove center portion between the ribs is not in contact with the anode and the cathode, electrons generated by the reaction disappear by electric resistance of the anode and the cathode before they reach the ribs, and there has also been a problem that it is difficult to make the reaction occur on the whole surface of the power generating cell.
Further, in the conventional solid electrolyte fuel cell disclosed in Japanese Patent Laid-Open No. 13088/1994, since part of or the whole of the reaction gas supply pipe is made of the relatively brittle ceramic pipe, the assembling operation must be performed carefully, so that an assembling operation time is increased, and there is a fear that the reaction gas supply pipe is damaged by thermal stress exerted on the reaction gas supply pipe by repetition of heat generation and cooling of the fuel cell.
An object in a first embodiment of the invention is therefore to provide a fuel cell module in which the whole surface of a power generating cell is made to contribute to the power generation so that power generation efficiency can be improved; to provide a fuel cell module in which oxidant gas is substantially uniformly made to flow to the whole of an oxidant electrode layer so that a power generating cell can be uniformly heated and cooled; to provide a fuel cell module in which the flow of fuel gas in a fuel electrode layer is controlled and a collision frequency between the fuel gas and the fuel electrode layer is increased, so that power generation efficiency can be improved; to provide a fuel cell module in which a heating-up time at start-up can be shortened, and damage of a power generating cell can be prevented by uniform temperature rising; to provide a fuel cell module in which fuel gas and oxidant gas are supplied to respective power generating cells at temperature suitable for power generation, so that power generation efficiency can be improved; to provide a fuel cell module in which one of or both of a fuel electrode current collecting body and an oxidant electrode current collecting body are joined to a separator made of stainless steel, an oxidant end plate, and a fuel end plate, and joined portions are welded to prevent oxidation of the joined portions, so that long electrical continuity between the separator, the oxidant end plate or the fuel end plate and the fuel electrode current collecting body or the oxidant electrode current collecting body can be obtained; and to provide a fuel cell module in which a reformer for reforming fuel gas is made unnecessary so that the number of parts can be decreased and miniaturization can be realized.
Besides, as the related art, there is disclosed a separator for a fuel cell formed into a shell structure in which the inside of a peripheral portion becomes hollow by integrally joining two thin separate plates each of which includes a center portion of a flat surface capable of receiving an electrode, and a peripheral portion bent to rise to one surface side (Japanese Patent Laid-Open No. 266776/1988). In this separator for the fuel cell, a supply and exhaust flow path hole of fuel gas and a supply and exhaust flow path hole of oxidizing gas are provided at the peripheral portions of the two separate plates. Besides, a structure is adopted such that the fuel gas flows to the flat surface of the center portion in the one separate plate, and the oxidizing gas flows to the flat surface of the center portion in the other separate plate. In the separator for the fuel cell constructed as stated above, the two separate plates are formed by press molding of thin plates, and these separate plates are integrated as one pair to form the separator, so that weight lightening can be realized. Besides, since the peripheral portion of the separator has the shell structure, mass production is easy, an error of an electrode size can be absorbed, and the sealing property of the fuel gas and the oxidizing gas can be improved.
However, since the separator for the fuel cell disclosed in Japanese Patent Laid-Open No. 266776/1988 has the shell structure having the hollow at the peripheral portion of the separator, there is a defect that the thickness of the separator becomes thick. An object of second and third embodiments of the invention is therefore to provide a structure for supplying gas to a fuel cell which can be made compact in a laminating direction of power generating cells by thinning a separator; and to provide a structure for supplying gas to a fuel cell in which fuel gas and oxidant gas supplied to a power generating cell can be controlled to have an optimum temperature for power generation.
Further, as the related art, there is disclosed a solid electrolyte fuel cell constituted by a base part in which a fuel electrode and an air electrode are provided on both surfaces of a solid electrolyte film, and a distributor is made of a material having the same composition as the solid electrolyte film, and a conductive part provided on a surface of the base part and made of a conductive material, wherein the solid electrolyte film is connected to an interconnector through the base part, and the air electrode and the fuel electrode are electrically connected to the interconnector through the conductive part (Japanese Patent Laid-Open No. 182680/1993).
In the solid electrolyte fuel cell constructed as stated above, since the base part of the distributor shows the same shrinkage behavior as the solid electrolyte film, separation of the distributor from the solid electrolyte film can be prevented against temperature rising/falling at the time of cosintering or operation, and warp of the distributor with respect to the solid electrolyte film can be prevented. Besides, since the same material as the material of the solid electrolyte film and mainly containing zirconia is used for the base part, it becomes an electric insulator. As a result, continuity between the front and back of the distributor is performed through the conduction part.
However, in the conventional solid electrolyte fuel cell, since the base part of the distributor which does not contribute to power generation is joined to the solid electrolyte film, there has been a defect that a surface area of the solid electrolyte film contributing to power generation is narrowed and power generation efficiency is lowered.
In order to solve this point, there is disclosed a solid electrolyte fuel cell in which an aggregate of a laminate composed of an anode, a solid electrolyte body, and a cathode and a separator provided with a reaction gas supply pipe are alternately laminated, a groove along which fuel gas flows is formed on one surface of the separator, and a groove along which oxidant gas flows is formed on the other surface of the separator (Japanese Patent Laid-Open No, 13088/1994). In this fuel cell, the reaction gas supply pipe is composed of a fuel gas supply pipe and an oxidant supply pipe, at least part of which is made of a ceramic pipe such as an alumina porcelain pipe. A structure is adopted such that the fuel gas supply pipe is connected to a side surface of the separator and communicates with the groove along which the fuel gas flows, and the oxidant supply pipe is connected to a side surface of the separator and communicates with the groove along which the oxidant gas flows. Alternatively, the fuel gas supply pipe is connected to a fuel gas distributor made of ceramic, and the oxidant supply pipe is connected to an oxidant gas distributor made of ceramic.
In the solid oxide fuel cell constructed as stated above, since the reaction gas supply pipes are individually connected to the respective separators, a circular glass ring or sealing a circular gas manifold formed for the aggregate and the separator can be made unnecessary, and a quadrangular glass ring for performing gas sealing between the aggregate and the separator can be made unnecessary.
However, in the solid oxide fuel cell disclosed in Japanese Patent Laid-Open No. 13088/1994, since part of or the whole of the reaction gas supply pipe is made of the relatively brittle ceramic pipe, the assembling operation must be carefully performed, the assembling operation time is increased, and there is a fear that the reaction gas supply pipe is damaged by thermal stress exerted on the reaction gas supply pipe by repetition of heat generation and cooling of the fuel cell.
Besides, in the conventional solid oxide fuel cell, there has also been a problem that it is very difficult to form the fuel gas distributor and the oxidant gas distributor out of ceramic, and further, they are easily affected by thermal expansion and thermal shock and are apt to be broken.
An object of a fourth embodiment of the invention is therefore to provide a distributor structure of a fuel cell module in which the whole surface of a power generating cell can be made to contribute to power generation, and respective separators connected to a distributor are electrically insulated by a comparatively simple structure, and further, an assembling operation time of a fuel short pipe and an oxidant short pipe can be prevented from increasing, and damage of the fuel short pipe due to thermal stress can be prevented.